1. Field of the Invention
The present invention relates to an image forming apparatus and more particularly, it relates to an image forming apparatus such as a multi functional printer which has a storage unit for storing image data and functions to form an image based on the image data stored in the storage unit.
2. Description of the Background Art
A method of erasing image data stored in a storage unit in a conventional image processing apparatus is disclosed in Japanese Unexamined Patent Publication No. 2004-214954, for example.
According to the Japanese Unexamined Patent Publication No. 2004-214954, an image processing method is disclosed in which an erasing operation is performed only in a FAT (File Allocation Table: file management information) and the image data is processed according to a degree of secrecy.
According to the Japanese Unexamined Patent Publication No. 2004-214954, since the processed image data remains in a storage unit of the image processing apparatus, the image data could be reproduced by restoring.
As a method to solve the above problem, Japanese Unexamined Patent Publication No. 2004-104581, for example, discloses an image forming apparatus in which image data is usually stored in a nonvolatile storage unit and the image data is stored in a volatile storage unit according to need. An erasing operation of the image data stored in the volatile storage unit is easy and it can be completed in a short time as compared with the nonvolatile storage unit. Furthermore, when power of the image forming apparatus is cut off, since contents of the volatile storage unit are erased, the image data does not remain in the image forming apparatus.
According to the Japanese Unexamined Patent Publication No. 2004-104581, it is necessary to erase the image data stored in the nonvolatile storage unit. Here, when the power of the image forming apparatus is cut off during its erasing operation, the erasing operation is not completed and the image data remains in the image forming apparatus.
In addition, since the volatile storage unit is expensive in general, when a high-capacity volatile storage unit is used for a normal image data storage, its cost becomes high.